It is well known that undesirable and costly polymerization is a significant problem during the manufacturing of various unsaturated monomers, particularly vinyl aromatic compounds, such as reactive dienes, specifically isoprene. In the purification of isoprene, reboilers on the extractive distillation absorber and stripper towers, and other equipment can experience fouling due to the presence of small oligomers (dimers/trimers/tetramers) of isoprene and cyclopentadiene, and large molecular weight free-radical polymers. The free-radical polymers are mixtures of linear and cross-linked isoprene and polymerized dimers.
Many kinds of inhibitors have been used in the past to minimize this problem. For instance, inhibitors such as diethylhydroxylamine, phenyl-p-phenylenediamines, tert-butyl catechol, and phenothiazine have been used to control polymer formation. During the early 1980s, compounds selected from the groups called alkyl-substituted di-nitro-phenols and nitroso-phenols found widespread use in the styrene industry. However, because such compounds also functioned as insecticides or were dangerous to handle, their use has been discouraged by environmental and government agencies.
It would be desirable if a composition and method could be devised to overcome some of the problems of the commercial polymerization inhibitors, and in particular to improve upon the performance of such prior inhibitors.